281 (number)

Source: Wikipedia, the free encyclopedia.
← 280 281 282 →
Cardinaltwo hundred eighty-one
Ordinal281st
(two hundred eighty-first)
Factorizationprime
Prime60th
Greek numeralΣΠΑ´
Roman numeralCCLXXXI
Binary1000110012
Ternary1011023
Senary11456
Octal4318
Duodecimal1B512
Hexadecimal11916

281 is the natural number following 280 and preceding 282. It is also a prime number.

In mathematics

281 is a

Eisenstein prime with no imaginary part, and a centered decagonal number
.

281 is the smallest prime p such that the

binary
, it has period length 70.

The generalized repunit number is composite for all prime p < 60000.

References

  1. ^ Sloane, N. J. A. (ed.). "Sequence A001359 (Lesser of twin primes)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
  2. ^ Sloane, N. J. A. (ed.). "Sequence A005384 (Sophie Germain primes p: 2p+1 is also prime)". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation.
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